1. Field of the Invention
This invention is directed to systems and methods for determining three-dimensional information about objects, such as their shapes, sizes, orientations and the like, and for systems and methods for controlling one or more processes or devices based on the determined three-dimensional object information.
2. Related Art
Suspension crystallization processes often result in crystals having a wide range of particle sizes. When crystallizing crystal-forming chemical compounds, controlling the particle size distribution (PSD) is typically highly important. For example, when the particle size distribution of high-aspect-ratio crystals is within a desired range, the efficiency of the downstream manufacturing process may be optimized or maximized. Likewise, when the particle size distribution of such high-aspect-ratio crystals is within a desired range, the overall quality of the end product being made, whether such high-aspect-ratio crystals are an intermediate product or the final end product, may be optimized or maximized.
Conventional techniques for determining the particle size distribution of a group of crystals include laser diffraction and laser backscattering, which are commonly-used on-line techniques. It should be appreciated that the drawbacks associated with these techniques discussed below are characteristic of the drawbacks associated with other techniques. T. Allen, “Particle Size Measurement, Vol. 1, 5th Edition”, Chapman and Hall, London, 1997, discusses the conventional techniques in detail.
Laser diffraction operates by passing laser light through a quantity of the suspended crystal particles. The diffracted laser beams are diffracted onto a CCD array or the like, where the diffraction patterns are captured. Based on the captured diffraction patterns, the crystal size and particle size distribution can be determined However, the analysis algorithms developed for analyzing the diffracted patterns have all been developed based on the assumption that the particles are spherical. Spherical particles make the analysis easy, because the diffraction patterns are independent of the orientation of the crystal particles and thus are solely dependent on the size of the crystal particles. Such orientation independence is obviously an appropriate assumption only for spherical particles, or near spherical particles, such as tetrahedrons, cubes and other near spherical orientation particles that can be treated as being generally orientation independent.
Because the measured size of many types of crystals, even such near-spherical crystals, is dependent on the orientation of the crystal particles, such laser diffraction methods are limited. Additionally, because the diffraction patterns are formed by passing light through a sample, such diffraction patterns are typically inappropriate for in-situ measurements or measurements of crystal solutions having high solids concentrations, where an insufficient amount of light would actually pass through the sample and be recorded. Thus, laser diffraction can over-estimate the broadness of the spherical diameter distribution, sometimes significantly, due to such orientation effects and the spherical models used to interpret the diffraction data.
In contrast to laser diffraction, which relies on light passing through the sample, laser backscattering relies on the particles reflecting a sufficient amount of light back towards the light source. Laser backscattering provides a chord length distribution that can be related theoretically to the particle size distribution. In laser backscattering, the laser beam is rotated over the particle slurry such that each particle backscatters light as the light passes over that particle. Based on a time-to-cross measurement and the known speed of movement of the laser beam, the chord length of the laser beam's path over the crystal can be determined. The chord length distribution can only be related back to the actual size distribution of the crystals by assuming some geometry for the particles, such as an aspect ratio, a specific orientation and/or the like. However, actual in-situ crystals have an infinite number of orientations. Moreover, the aspect ratio, i.e., a length to thickness, of the crystals is one of the variables that appropriate control of the crystallization process affects. Accordingly, assumptions about the crystals' geometry render the laser backscattering analysis less than complete.
As a result of the shortcomings of laser diffraction and laser backscattering, various imaging-based systems have been developed to size high-aspect-ratio, i.e., elongated, crystals. Such imaging systems and techniques offer the potential to extract both size and shape information. Thus, such imaging based systems and techniques are a promising and attractive approach for obtaining particle size distributions for non-spherical particles. Conventional, imaging-based, on-line particle size and shape analyzers are available from Malvern and Beckman-Coulter, such as the Malvern Sysmex FPIA3000 and the Beckman-Coulter RapidVUE. Powder Sampling and Particle Size Determination, by T. Allen, Elsevier, 2003, surveys other imaging-based instruments.
Typically, these instruments require withdrawing a sample of the crystal slurry from the crystallization reaction vessel. Drawing such samples is inconvenient, possibly hazardous, and raises concerns about whether the sample is truly representative of the bulk slurry. One notable system that provides for in-situ sampling is the Particle Vision and Measurement (PVM) system from Lasentec, Inc. The Lasentec Particle Vision and Measurement in-situ probe is combined with automatic image analysis software that is useful for some types of crystals. However, this system does not give suitable results for high-aspect-ratio crystal particles.
U.S. patent application Ser. No. 11/237,088, which is assigned to the same assignee as the present application and which is incorporated by reference herein in its entirety, discloses systems and methods for determining a particle size distribution by obtaining and analyzing an in-situ image of the crystallization process. In particular, the 088 patent application determines a length measurement for each located crystal. A crystal is located by finding line segments within the obtained in-situ image. Line segments that appear to be part of a single crystal edge are combined to form virtual lines. Parallel line segments and/or virtual lines that meet defined relationships are identified as the edges of a given crystal. Connected components associated with the parallel line segments and/or virtual lines are combined, and a length of the combined connected component is the length size of that given crystal.